Ion producing apparatus



15, 1955 H. P. YOCKEY 2,715,694

- ION PRODUCING APPARATUS Filed May 9, 1947 /0 EZE. 8.

IN VEN TOR. Hubert I? we-key mMJMA;

United States Patent Office Patented Aug. 16, 1955 ION Pnonncmc arranaros Hubert P. Jockey, ingiewood, Caiifi, assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application May 9, 1947, Seriai No. 747,863

13 Claims. Ii. 313-3) This invention relates generally to ion producing apparatus, and more particularly, to improvements in ion producing apparatus of the type which is particularly applicable for use in an electromagnetic isotope separating unit commonly known as a calutron.

in such calutrons, a beam of positive ions of the charge material, the isotopes of which it is desired to separate,

is formed and projected at a high velocity into an evacuated tank region traversed by a substantially uniform magnetic field perpendicular to the direction of projection of the ion beam. Due to the influence of the magnetic field upon the moving charged particles, each particular ion is caused to describe a circular path having a radius proportional to the square root of its mass. As a result, the original singie ion beam is split into more or less distinct component beams, each consisting solely of ions of a particular mass weight. Because of a geometric focusing action, these component isotopic beams are most distinctly resolved after the completion of 180 of their circular path, and the individual isotopes may be separately collected at a suitable receiver located at this point.

Perhaps the most critical portion affecting the operation of such a calutron unit is that portion concerned with the production of positive ions of the charge material and the projection thereof in the form of an ion beam. conventionally such apparatus comprises a hollow elongated chamber having an inlet extending along one entire side thereof through which vapor of the charge or source material is permitted to enter. Opposite this inlet, and extending substantially the entire length of the chamber, is a slit-iike aperture through which the ionized particles are withdrawn in the form of a beam. At one end of this chamber there is disposed a small slot through which an ionizing electron stream enters the ionization chamber to bombard and thus ionize the vaporized molecules of the charge material. A filamentary cathode is positioned adjacent this slot and external to the chamber to provide the primary electrons for this ionizing discharge.

One problem which is encountered in the operation of such ion producing apparatus is the repid deterioration of the filamentary cathode. In operation, the filamentary cathode is subject to intense bombardment by the positive ions of the charge material which are formed in the electron stream. In the most common present use of a calutron unit, the charge material contains uranium, and accordingly, the filamentary cathode is subject to bombardment by the very heavy uranium ions, resulting in rapid Wear and breakdown of the filamentary cathode itself. For the foregoing reasons, it is found that in the operation of a calutron unit, frequent replacement of the filamentary cathode is required. This is not only undesirable by reason of the initial cost of the filamentary cathode itself, but more particularly, by reason of the loss of operating time required to replace the cathode, and the complications in overall design incident to the provision of means for replacing the cathode while maintaining the high vacuum within the unit.

A more important difliculty encountered in the operation of such ion producing apparatus is that of maintaining a steady non-hashy ionizing electric discharge along the entire length of the ionization chamber. It will be apparent that if the ionizing arc is hashy or irregular, the positive ion beam, itself, also becomes erratic. This, of course, results in poor separation and reception of the individual isotope beams. In the past, in order to overcome instability in the operation of the ionizing arc, it has been necessary to increase the supply of source material vapor into the ionizing chamber by increasing the operating temperature and thus increasing the charge vapor pressure. Such an increase in the vapor pressure of operation of the ionization chamber is accompanied by many undesirable efiects. The higher the pressure of operation, the greater is the ratio of unionized to ionized particles which spew out of the ionization chamber and into the tank separating region. Unionized particles which are present in the separating region interfere with the ion beam, itself, thus causing scattering of the beam and poor separation and collection of the isotopes; deposit on the tank Walls and accelerating electrodes thus changing critical dimensions and providing a cleaning and recovery problem; and reduce the overall efiiciency of operation from loss of charge material. Further, when operation is carried on at higher operating pressures, there are availabie more positive ions of the charge material to bombard the filamentary cathode, thus increasing the rate of wear and corrosion and reducing the life of the cathode.

For all of the above reasons and many other incidental reasons, it would obviously be desirable to be able to provide an extremely stabie and steady ionizing arc at a low charge vapor pressure. The present inventor has conceived that substantial improvement in the stability and uniformity of the ionizing arc can be obtained by the introduction of an auxiliary gas into the electron stream at the anode end thereof, thus providing additional positive ions to support the discharge and to new tralize the space charge of the electron stream. it has been found that in this manner a steady ionizing arc can be obtained in an ionization chamber which is run colder and at a lower charge vapor pressure than was heretofore required, thus reducing charge consumption; reducing gunking or depositing of charge material on portions of the unit; providing a steady uniform positive ion beam; prolonging the life of the filamentary cathode; and generally increasing the efiiciency of separation and collection of the component isotopes of the charge material.

Accordingly, it is the primary obiect of the present invention to provide improved ion beam producing apparatus particularly adapted for use in a calutron.

Another object of the present invention is to provide ion producing apparatus of the type utiiizing an ionizing electric discharge, wherein an auxiliary gas is introduced into the electric discharge at the anode end thereof for the purpose of improving the stability of the discharge.

Other objects and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings, wherein Fig. l is a plan view, partially in section. of ion producing apparatus constructed according to the principles of the present invention; and

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

Referring now to the drawings, the ion producing a paratus itself embodies three separate but communic 'ng chambers, namely a vaporizing chamber 1, an ionization f in the ionization chamber. maintained at a'high negative potential with respect to T the ion producing apparatus proper by means of a suitable source of direct voltage, indicated schematically by battery chamber 2, and an auxiliary gas chamber 3. r This whole apparatus normally occupies a position at the bottom of the front side of a conventional calutron unit. The positive ions formed in the ionization chamber 2 are withdrawn in the form of an ion beam, schematically indicated at 8, through an elongated slot 4 by the accelerating electrodes, which electrode also has a slot 6 adjacent slot 4 Accelerating electrode 5 is 7. Thus, the ions are withdrawn from the ionization 5 chamber 2'in the form of beam 8, which beam traverses 3 the ;slot 6 in accelerating electrode 5," and due to the influence of the transverse magnetic field, indicated schematically at H, describes a circular path about a horizontal i axis, and is simultaneously separated into component isotope beams, which are separately collected in suitable receiving apparatus normally positioned at the top of the f front side of the calutron unit. 7

g The vaporizing chamber 1, which may be rectangular I in shape, as shown, contains a suitable amount of charge materialin its solid form, as schematically indicated at 10. At the top of the vaporization chamber 1 there is provided a suitable heating element, schematically indicated by coil 15,.which serves to heat the charge material to its vaporization point, whereuponthe vapor of the charge material ditfuses through an elongated slot 14 in one side 1 of the vaporization chamber 1 into the ionization chamber 2;

A filamentary cathode 16, which is preferably shaped as a U, is disposed externally to the ionization chamber 2 'on the right end thereof'as viewed in'Fig. lfi. Filamentary cathode 16 may be supported in an insulated manner 1 from the outer surface of the vaporizing chamberl', as indicated by insulating support 21 to which both legs of Q the U-shaped cathode may be attached. A collimating slot is formed in the right end of the ionization chamber .at 19. The slot at 19 and the base of the cathode U are aligned, both extending into the paper, as viewed in Fig. 1.

Opposite terminals of filamentary cathode 16 are connected to spaced points near the positive side of battery 7,

l as by leads 17 and 18'; ltwill be apparent, therefore, that the filamentary cathode 16 as a whole is maintained at a small negative potential with respect to the ion producing apparatus proper with the result that the ion producing apparatus becomes an anode for cathode 16. The

the charge material, which ions are then' withdrawn through slot 4 in the form of a beam by accelerating electrode 5 as was previously explained.

According to the principles of the present invention, an auxiliary gas chamber 3 is provided on the left end of the ionization chamber 2, as viewed in Fig. 1. Auxiliary In operation, the auxiliary gas introduced into auxiliary chamber 3 diffuses through collimating slot 24mm and along the ionization chamber 2, and more particularly along the ionizing electron stream 29 in a direction opposite to that of the electrons. The atoms of this auxiliary gas are also ionized by electron stream 20, whereby additional ions are provided to support the discharge itself and to neutralize the space charge of the discharge. In this manner, it has been found that the ionizing electric discharge is rendered substantially more stable than is 7 otherwise possible, resulting in the numerous advantages previously mentioned.

Although manytdifferent gases could be employed as the auxiliary gas to effect to some degree the. abovedescribed advantages, the characteristics of the auxiliary gas for greatest effectiveness are lightness and stability.

It will be apparent that if an auxiliary gas of low atomic weight is utilized, it will readily difiuse through the, collimating slot 24 out into and along the ionizing electron stream 20, and thus be in a position to accomplish its purpose in stabilizing the electric discharge. Also, the

lighter the auxiliary gas employed, the smaller will: be'

its eiiect in scattering the ion beam, itself, in the tank region. With respect to the longevity of the cathode 16,

it is desirable for the auxiliary gas to be as light as possible in order that erosion of cathode 16 dueto bombardment by positive ions of this gas will be small. It is also desirable that the gas employed be-highly stable, preferably an inert gas, so that it will not react with the cathode 16 and with other portions of the calutron unit, thereby facilitating cleaning and chemical recovery after a run has been completed. Other gases, besides helium, which are particularly well suited forthe purposes to be served are argon, neon, nitrogen, and hydrogen.

Since many changes in the above construction and many apparently widely different embodiments of' the invention could be made without departing from the scope thereof,

it is intended that all matter contained in the above'description, or shown in the accompanying drawings, shall be interpreted as illustrative andnot in a limiting sense;

What is claimed is: V lxApparatus for developing gaseous ions comprising an'ionization chamber, means for traversing said chamber with an ionizing electron stream, means for introducing the gas to be ionized into said chamber, and means disposed at the anode end of said electron stream for introducing into said chamber a gas different from the gas to be ionized. a

2. Apparatus for developing gaseousions of a source material comprising an ionization chamber, means for traversing said chamber with an ionizing electron stream,

gas chamber 3 and ionization chamber 2 communicate a with each other by means of a second collimating slot 24, which may be identical to the previously described collimating slot at 19 both with respect to shape and alignment. Thus, since collimating slot 24, occupies that portion of the left end of the ionization chamber 2 upon which the ionizing electron stream 20 would otherwise impinge, the electron stream 20 proceeds through slot 24 and traverses the auxiliary gas chamber 3. An auxiliary gas inlet tube 22 projects into the interior of auxiliary gas chamber 3 through a suitably sealing arrangement, schematically indicated at 23. The exterior end of tube 22 is connected to a suitable source, not shown, of the auxiliary gas, such as helium. which is to be used.

means for introducing vapor of the source material into said chamber to be ionized by said electron stream, and means for introducing an auxiliary gas into said chamber at the anode end of said electron stream.

3. Apparatus for developing gaseous ions of a source material comprising an ionization chamber, means for traversingsaid chamber with an ionizing electron stream,

means for introducing vapor of the source material into said chamber to be'ionized by said electron stream, and means for introducing an auxiliary gas into'said electron stream at the anode end thereof.

4. Apparatus for developing gaseous ions of a source material comprising an ionization'chamber, means for traversing said chamber with an ionizing electron stream,

means disposed along the length of said electron stream for introducing vapor of the source material into said chamber to be ionized by said electron stream, and meansdisplaced at the anode end of said electron stream for introducing an auxiliary gas into said chamber. 7

5. Apparatus for developing gaseous ions of a source. material comprising an ionization chamber, means for.

traversing said chamber with an ionizing electron stream, means disposedalong the length'ofsaid electron stream for introducing vapor of the source material into said chamber to be ionized by said electron stream, and means disposed at the anode end of said electron stream for directing an auxiliary gas into and along said electron stream.

6. Apparatus for developing gaseous ions of a source material comprising an ionization chamber, means for traversing said chamber with an ionizing electron stream, means for introducing vapor of the source material into said chmnber in a direction transverse to said electron stream to be ionized by said stream, and means for introducing an auxiliary gas into said chamber in a direction opposite to the flow of electrons in said electron stream.

7. Apparatus for developing gaseous ions of a source material comprising an ionization chamber, means for traversing said chamber with an ionizing electron stream, a first and a second gas inlet for said chamber disposed at difierent positions with respect to said electron stream, the second of said inlets being disposed at the anode end of said electron stream, means for introducing a vapor of the source material into said chamber through the first of said inlets to be ionized by said electron stream, and means for introducing an auxiliary gas into said chamber through the second of said inlets.

8. Apparatus for developing gaseous ions from a vaporizable source compound comprising means defining an elongated restricted region for gas ionization having a slit like aperture extending in the direction of its elongation and substantially coextensive therewith, means for directing a stream of accelerated electrons from one end of said region to the other end thereof, means for introducing into said region intermediate the ends thereof a vapor of said source compound, means for introducing an auxiliary gas into said electron stream adjacent said other end of said elongated region, and means for withdrawing ion sof said vapor from said region through said slit-like aperture along the entire length thereof.

9. Apparatus for developing gaseous ions from a vaporizable source compound comprising means defining an elongated restricted region for gas ionization having a slitlike aperture extending in the direction of its elongation and substantially coextensive therewith, means for introducing a vapor of said source compound into said region intermediate the ends thereof, means for establishing an arc discharge through said region in the direction of its elongation to establish a discharge path containing positive ions of said vapor, means for introducing into said discharge path at the anode end thereof an auxiliary gaseous medium, and means for withdrawing ions of said vapor from said region through said slitlil-:e aperture along the entire length thereof.

10. Apparatus for developing gaseous ions comprising an ionization chamber containing molecules of the gas to be ionized, said chamber having a slot at one end thereof, an auxiliary gas chamber adjacent to said ionization chamber and communicating therewith by means of said slot, means for establishing an arc discharge traversing said ionization chamber and extending through said slot, and means for introducing an auxiliary gas into said auxiliary chamber, said auxiliary chamber being disposed at the anode and of said are discharge.

11. Apparatus for developing gaseous ions comprising an ionization chamber containing molecules of the gas to be ionized, said chamber having a slot at both ends thereof, an auxiliary gas chamber adjacent said ionization chamber and communicating therewith by means of one of said slots, a source of electrons disposed externally to said ionization chamber and substantially contiguous with the other of said slots, means for accelerating electrons from said source to form an electron stream traversing said ionization chamber and extending through both of said slots, and means for introducing an auxiliary gas into said auxiliary chamber.

12. Apparatus for developing gaseous ions comprising an ionization chamber containing molecules of the gas to be ionized, said chamber having a slot at both ends thereof, an auxiliary gas chamber adjacent said ionization chamber and communicating therewith by means of one of said slots, a source of electrons disposed externally to said ionization chamber adjacent the other of said slots, means for establishing a magnetic field traversing said chamber and extending through said slots, means for maintaining said ionization and auxiliary chambers electrically positive with respect to said electron source, whereby an arc discharge is established in a direction parallel to said magnetic field, and means for introducing into said auxiliary chamber an auxiliary inert gas having a lower atomic weight than the gas to be ionized.

13. Apparatus for developing gaseous ions of a material having a high atomic weight comprising an ionization chamber containing molecules of the gas to be ionized, said chamber having a slot at both ends thereof, an auxiliary gas chamber adjacent said ionization chamber and communicating therewith by means of one of said slots, at source of electrons disposed externally to said ionization chamber adjacent the other one of said slots, means for establishing a magnetic field traversing said chamber and extending through said slots, means for maintaining said ionization and auxiliary chambers electrically positive with respect to said electron source, whereby an are discharge is established in a direction parallel to said magnetic field, and means for introducing into said auxiliary chamber an inert gas of low atomic weight.

14. Apparatus for developing gaseous ions of a material having a high atomic weight comprising an ionization chamber containing molecules of the gas to be ionized, said chamber having a slot at both ends thereof, an auxiliary gas chamber adjacent said ionization chamber and communicating therewith by means of one of said slots, at source of electrons disposed externally to said ionization chamber adjacent the other one of said slots, means for establishing a magnetic field traversing said chamber and extending through said slots, means for maintaining said ionization and auxiliary chambers electrically positive with respect to said electron source, whereby an arc discharge is established in a direction parallel to said magnetic field, and means for introducing helium gas into said auxiliary chamber.

15. Apparatus for developing gaseous ions from a vaporizable source compound comprising means defining an elongated restricted region for gas ionization having a slit-like aperture extending in the direction of its elongation and substantially coextensive therewith, means for introducing a vapor of said source compound into said region intermediate the ends thereof, means for establishing an arc discharge through said region in the direction of its elongation to establish a discharge path containing positive ions of said vapor, a separate gas chamber adjacent said region at the anode end of said arc discharge, said chamber having a collimating slot accommodating said are discharge, means for introducing an auxiliary gas into said chamber, and means for withdrawing ions of said vapor from said region through said slitlike aperture along the entire length thereof.

16. Apparatus for developing gaseous ions from a vaporizable source compound comprising means defining an elongated restricted region for gas ionization having a slitlike aperture extending in the direction of its elongation and substantially coextensive therewith, a separate gas chamber adjacent one end of said region and communicating therewith by means of a common opening therebetween, an electron source at the other end of said region, means for establishing an arc discharge from said electron source along the entire length of said region and through said opening and into said separate chamber, means for introducing into said region intermediate the ends thereof a vapor of said source compound, means for introducing an auxiliary gas into said separate chamber, and means for withdrawing ions of said vapor from said region through said slit-like aperture along the entire length thereof. 7

l V 17. Apparatus for developing gaseous ions from a vaporizable source compound, comprising means defining an elongated region for gas ionization, means for introducing into said region a vapor of said compound, means for esi tablishing an arc discharge through said region in the digjrection of its elongation'to provide a discharge path conjtaining positive ions of said vapor throughout said region ;'and means for directing the flow of auxiliary gaseous medium into said region at the anode end of said discharge path.

18. Apparatus for developing gaseous ions from a vaporizable source compound comprising means for establishing an arc discharge, said means comprising an elongated are chamber including'means constituting an Ianode for said are discharge and an electron emissive cathode for said arc discharge positioned at one end of 7 said chamber, means directing the flow of electrons lengthwise of said chamber from said cathode, means for effect ing a flow of vapor of said compound into said chamber to provide an arc discharge containing positive ions of said vapor, means for introducing into said discharge an auxiliary gas, and means for directing the flow of said 7 auxiliary gas through said region in a direction opposite the flow of said electrons, said chamber having aslit-like aperture extending in the direction of its elongation sub stantially co-extensive therewith, and means for withdrawing ions of said vapor from said region through said slit-like aperture along the entire length thereof.

No references cited. 

1. APARATUS FOR DEVELOPING GASESOUS IONS COMPRISING AN IONIZATION, MEANS FOR TRAVERSING SAID CHAMBER WITH AN IONIZING ELECTRON STREAM, MEANS FOR INTRODUCING THE GAS TO BE IONIZED INTO SAID CHAMBER, AND MEANS DISPOSED AT THE ANODE END OF SAID ELECTRON STREAM FOR INTRODUCING INTO SAID CHAMBER A GAS DIFFERENT FROM THE GAS TO BE IONIZED. 